I. Field of the Invention
This invention relates to a novel lactam-containing emulsifier system for water-in-oil emulsion polymers. It further relates to a method for carrying out an inverse emulsion polymerization, and product obtained therefrom.
II. Description of the Prior Art
A variety of water-soluble polymers are produced by precipitation polymerization. Typical of such polymers are crosslinked polyacrylic acid, such as, the Carbopol.RTM. resins of B.F. Goodrich, which have been widely used as thickeners for aqueous systems. The unique thickening efficiency and rheological properties of these resins are attributed to the incorporation of an allyl crosslinker, such as, polyallyl sucrose or polyallyl pentaerythritol. With this technique, the polymer is usually produced in an organic solvent, e.g., benzene or ethyl acetate, from which it precipitates and is recovered in the form of a powder. This presents a number of problems. For example, often residual organic solvent as well as unreacted monomer may be retained in the separated resin particles. For most end uses, these residual materials cannot be tolerated. In particular, these polymers are often used as thickeners in personal care products. The presence of such toxic solvents or monomers renders the polymer unusable for this purpose, unless it is first treated to remove the impurities. Such treatments not only increase processing time, but significantly increase the processing cost.
Additionally, because the polymeric product is obtained in particulate form, and since it is normally utilized because of its water-soluble properties, the particles must again be redissolved into the end use composition. Such mixing and redissolving generally require rather complex mixing equipment which often is not available at the site of end use.
Additionally, the polymer is obtained in acid form and must be neutralized before it can be used in a personal care product. The neutralization step is required to obtain the thickening properties of the polymer. This again requires another processing step, adding to the cost of the use of the product.
Another important process for making water-soluble polymers on a production scale is inverse emulsion polymerization. However, the water-in-oil emulsion polymers obtained from this process often contain small amounts of unreacted monomers and hydrocarbon oils which may not be of the highest purity. The monomer and hydrocarbon oil toxicity and offensive odor prevent such polymers from being used in personal care and health care products.
In a typical inverse emulsion polymerization, a water-in-oil monomer emulsion is produced by adding a water phase of an aqueous solution of monomers, to an oil phase containing an oil-soluble surfactant under rapid agitation. The monomer emulsion is then homogenized to obtain the proper particle size and then subjected to polymerization conditions to form a water-in-oil polymer emulsion using a water-soluble or water-insoluble initiator. Thereafter, a high HLB value surfactant is incorporated into the polymer emulsion to convert it into an oil-in-water system. This inverse emulsion polymerization process has the advantages of producing polymers of a high molecular weight at a high polymerization rate compared to polymer from a typical solution or precipitation polymerization process of the same monomer.
Although the inverse emulsion polymerization process has the above noted advantages many problems, such as, poor emulsion stability, incomplete polymerization, difficulty of self-inversion, and high oil contents in the products remain to be solved.
A variety of emulsifiers (surfactants or surface active agents) are used for the emulsification, sorbitan monooleate being one of the most popular and readily available. While these form stable emulsions, the polymer emulsion has a very high bulk viscosity and is very difficult to be self-inverted in water.
United States patents relating to the foregoing include:
U.S. Pat. No. 3,826,771 discloses the use of sorbitan monooleate and sorbitan monostearate as the water-in-oil emulsifying agents. PA1 U.S. Pat. No. 3,278,506 discloses the use of ethylene oxide condensates of fatty acid amides as the emulsifiers. PA1 U.S. Pat. No. 4,024,097 discloses the use of surfactant systems consisting of an oil-soluble alkanolamide (e.g. Witcamide 511, Witco Chemical) and one or more co-emulsifiers of unesterified dialkanol fatty amide, salts of fatty tertiary amines, quaternized ammonium salts of fatty tertiary amines, alkali metal salts of fatty acids, and alkyl or alkyl aryl sulfates or sulfonates. PA1 U.S. Pat. No. 4,672,090 and 4,772,659 both disclose a surfactant system for water-in-oil emulsions comprising an oil-soluble alkanolamide, a polyoxyethylene derivative of a sorbitan ester, and sorbitan monooleate. PA1 R.sub.1 is a linear, branched or cyclic alkyl having from 6 to 18 carbon atoms with the proviso that at least one of R or R1 must contain at least six carbon atoms and the sum of the carbon atoms in R and R.sub.1 cannot exceed 18; and PA1 n is 3, 4, or 5. PA1 R.sub.2 is hydrogen or a linear, branched, or cyclic alkyl having from 1 to 30 carbon atoms and may vary between different --(CHR)-- groups; PA1 with the proviso that at least one of R.sub.2, R.sub.3, or R.sub.4 is alkyl; PA1 n is 3, 4 or 5; and PA1 x is such that the molecular weight of the polymer is from about 2,000 to 20,000.